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Health ConsultationCADDO LAKE AREAMERCURY EXPOSURE INVESTIGATIONCADDO LAKE AREA, HARRISON COUNTY, TEXASMARCH 21, 2005U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICESPublic Health ServiceAgency for Toxic Substances and Disease RegistryDivision of Health Assessment and ConsultationAtlanta, Georgia 30333

Health ConsultationMercury Exposure InvestigationCaddo Lake AreaHarrison County, TexasPrepared by:The Texas Department of State Health ServicesUnder Cooperative Agreement withU.S. Department of Health and Human ServicesAgency for Toxic Substances and Disease Registry

Health ConsultationMercury Exposure Investigation – Caddo Lake AreaTable of ContentsSummary and Statement of Issues . 2Background . 3Site Description and History. 3Rationale for an Exposure Investigation. 4Methods. 4Participants. 4Collection of Blood Samples for Mercury Analysis. 5Aquatic Sampling and Analysis. 5Results. 5Discussion . 7Public Health Implications. 7Conclusions. 8Public Health Action Plan. 9Actions Completed. 9Actions Recommended . 9Actions Planned . 9Authors, Technical Advisors, and Organizations . 10References. 11Appendices. 13Appendix A: - Acronyms and Abbreviations . 14Appendix B: - Figures. 16Appendix C: - Tables . 21Attachments . 26Attachment A—Participant Consent for Blood Specimen Testing . 27Attachment B—Caddo Lake Fish Consumption Survey . 301

Health ConsultationMercury Exposure Investigation – Caddo Lake AreaSummary and Statement of IssuesThe Texas Department of Health (TDH), now the Texas Department of State Health Services(DSHS), issued a consumption advisory for largemouth bass and freshwater drum from CaddoLake in 1995 due to elevated levels of mercury in the fish. In 2003, DSHS began receivinganecdotal reports from a community group that people, possibly including subsistence fishers,continued to eat these species of fish from Caddo Lake. The purpose of this investigation, whichwas conducted from May 11, 2004 through May 15, 2004, was to assess whether people who eatfish from Caddo Lake were potentially being exposed to harmful amounts of methylmercury(MeHg).Blood mercury levels were measured in 71 voluntary participants. At the time the blood wascollected, each participant was asked about the types of fish they ate, how often they ate fish, andthe locations from where the fish they ate were caught. The fish catch locations supplied by theparticipants were used to determine possible lake area sites for obtaining additional fish tissuesamples.The primary objectives of this exposure investigation were to: Provide people who consume fish taken from Caddo Lake the opportunity to have anassessment of their current exposure to mercury through confidential, independentlaboratory testing of their blood. Obtain information regarding the types of fish consumed and the locations from whichthe fish were caught to identify fish sampling needs for laboratory analysis. Use blood mercury concentrations to determine whether the participants were beingexposed to mercury at levels that have been associated with adverse health outcomes. If required, provide individuals with scientifically based guidance on how they mightreduce their exposure to mercury. Assess whether additional efforts are needed in the community to reduce potential healthrisks.2

Health ConsultationMercury Exposure Investigation - Caddo Lake AreaBackgroundSite Description and HistoryCaddo Lake, located in the northeastern part of the state, is the only naturally occurring lake inTexas. The western part of the lake is in Texas and the eastern portion is in Louisiana [Figure 1].The lake covers 26,810 acres, has a maximum depth of 20 feet and an average depth of 8-10 feet[1, 2]. The Caddo Lake habitat, described as a wetland having both bottomland hardwoods andbald cypress swamps, supports the largest populations of certain duck species and the mostdiverse fish fauna in Texas [3]. In October 1993, the Ramsar Convention on Wetlandsdesignated the lake as a Wetlands of International Importance [4].The communities nearest to the lake include the cities of Karnack (population 775) andUncertain (population 150) [5]. On the southwestern side of the lake is the former LonghornArmy Ammunition Plant (LAAP), a 8,493 acre U.S. government-owned facility that operatedintermittently from 1942 to 1997, producing 2,4,6-trinitrotoluene (TNT), pyrotechnicammunition, rocket motors, and plastic explosive. LAAP was placed on the U.S. EnvironmentalProtection Agency (EPA) National Priorities List (NPL) on August 30, 1990. The Agency forToxic Substances and Disease Registry (ATSDR) prepared a Health Assessment for LAAP inJuly 1999 and concluded that the site poses no apparent public health hazard because people arenot likely to come in contact with site contaminants or because institutional controls aresufficient to protect human health [6]. Mercury was not used at LAAP and has not been detectedin its permitted discharge [3]. On May 5, 2004, administrative control of approximately 5,000acres of the LAAP site was granted to the U.S. Fish & Wildlife Service as the Caddo LakeNational Wildlife Refuge. The U.S Army retains control of the remainder of the site [7].On November 2, 1995, due to elevated levels of mercury in fish1, the DSHS issued aconsumption advisory for largemouth bass (Micropterus salmoides) and freshwater drum(Aplodinotus grunniens) taken from Caddo Lake. The consumption advisory states that eatingbass or drum from the lake should be limited to two 8-ounce meals per month for adults and two4-ounce meals per month for children [8]. More frequent consumption of fish or consumption ofgreater quantities of fish than recommended by the advisory may pose a potential human healthrisk, particularly to children and women of child bearing age.Recently, the DSHS Exposure Assessment and Surveillance Group began receiving anecdotalreports from a community group that people, possibly including subsistence fishers, were eatingthe species of fish named in the advisory. In response to these reports, DSHS conducted anexposure investigation to evaluate current exposure to methylmercury through confidentiallaboratory testing of blood and updated fish sampling and tissue analysis. From May 11 to May15, 2004, DSHS collected blood samples from 71 people (8 to 88 years of age) most of whomregularly eat fish from Caddo Lake. Additionally, from May 25 to May 27, the DSHS Seafood1The mercury in the lake is believed to be from atmospheric deposition of non-point source emissions. Possible sources for the emission ofmercury could be coal-fired power plants. Caddo Lake has conditions favorable for the uptake and biomagnification of methylmercury in thefood chain. These include: low pH, high dissolved organic carbon, and high sulfate [3].3

Health ConsultationMercury Exposure Investigation - Caddo Lake Areaand Aquatic Life Group collected fish and frogs from Caddo Lake at locations identified by theparticipants in the Exposure Investigation as areas where they obtain their fish.Rationale for an Exposure InvestigationAssessment of exposure usually is accomplished by looking at contaminant concentrations andpathways of exposure to construct exposure scenarios which are used to estimate the amount ofthe contaminant that gets into the body. The resulting exposure estimates often are made withconsiderable scientific uncertainty. When dealing with fish eating populations, this uncertaintyis exacerbated by several factors; the mixture of fish species in the diet, the portion size of thefish meal, and the interaction of the frequency of fish consumption with the kinetics of mercuryelimination from the body. Directly measuring the level of a substance of concern in the body isa more direct way to assess whether exposure is occurring. In the past, mercury was found inlargemouth bass and freshwater drum at levels high enough to warrant issuing a consumptionadvisory for these species. The purpose of this exposure investigation was to assess individualexposure to mercury among people who regularly consume fish from Caddo Lake. Becauselong-term consumption of fish is the presumed exposure scenario, and blood mercury levels peaksoon after exposure, DSHS tested for mercury in blood as a measure of recent exposure.MethodsParticipantsDSHS obtained a list of potential participants from a local minister and the Caddo Lake Institute(a private non-profit foundation). The DSHS also placed announcements in local newspapers,sent flyers to local government officials to post in their respective cities, and contacted localofficials to help recruit volunteers. DSHS contacted potential participants by telephone to solicitparticipation. Participants either traveled to City Hall in Uncertain, Texas or received a visitfrom DSHS staff that traveled throughout the lake area to collect blood samples at privateresidences, businesses, boat docks, and highway right-of-ways.To assess exposure to mercury, DSHS collected blood from 71 volunteer participants who signeda consent statement agreeing to the testing (Attachment A). Participants reviewed and signed amedical release form which allowed DSHS to collect a blood sample. Educational materialcontaining information on how to reduce exposure was distributed to each participant.During the blood sample collection, a brief questionnaire (Attachment B) was completed witheach participant. Participants were asked questions about the length of time they had lived in thecommunity, the types of fish they consumed from the lake, and how often they consumed fishfrom the lake. The participants also were asked about the locations from where the fish theyconsumed were caught [Figure 2]. Information concerning the catch locations was given to theDSHS Seafood and Aquatic Life Group to help determine sampling sites for updated fish tissueanalysis.4

Health ConsultationMercury Exposure Investigation - Caddo Lake AreaBlood samples were collected from 34 males (48 %) and 37 females (52 %). The age range ofmales was 8 to 86 years of age. The age of the females ranged from 18 to 88 years. The averageages of male and female participants were 52 and 59 years old, respectively. Three of theparticipants indicated that they did not eat fish or had not eaten fish taken from Caddo Lakewithin approximately 4 years.Collection of Blood Samples for Mercury AnalysisAll blood draws were conducted using clinical standards. Public health nurses from the DSHSRegion 4 office in Tyler, Texas collected venous blood samples using 7 milliliter (mL)Vacutainer tubes containing heparin. DSHS Exposure Assessment and Surveillance staffmaintained chain of custody during the labeling, packaging and shipping of the samples toClinical Pathology Laboratory in Austin, Texas. Specialty Laboratories, Inc., Santa Monica,California analyzed the samples for total mercury (methyl and inorganic mercury).Aquatic Sampling and AnalysisOn May 25-27, 2004, the DSHS Seafood and Aquatic Life Group collected fish and frog fromsample locations identified by the participants in the exposure investigation. They usedelectrofishing5, trap nets, and gill nets to collect the fish while bullfrogs (Rana catesbeiana) werecollected by hand at night using spotlights. A total of 66 samples were collected and the tissuewas analyzed for total mercury by the DSHS laboratory in Austin, Texas using EPA Method245.6 (total mercury in tissues) [9]. Only the edible muscle tissue from each fish and frog wasretained for analysis.Bullfrog (n 6) and nine different types of finfish were collected to represent the types of aquaticlife eaten by people in the area. The types of fish caught are largemouth bass (n 14), bream(n 8), catfish (n 9), pickerel (n 2), crappie (n 14), freshwater drum (n 6), gar (n 1),warmouth/goggle eye (n 4), and white bass (n 2). The data, by species, are shown in Table 1.The average total mercury concentration varied among the different species ranging from 0.116parts per million (ppm) for bullfrog to 1.16 ppm for gar. The highest single total mercury levelwas found in a largemouth bass (1.77 ppm). The lowest single total mercury level was found ina catfish (0.0647 ppm).ResultsIndividual test results and a written explanation of their meaning were provided to eachparticipant. A DSHS physician and a toxicologist were available to discuss individual results bytelephone. Recommendations for follow-up actions were made as appropriate. In accordancewith state confidentiality law, individual test results were not made available to the generalpublic.5Electrofishing is a fish collection method in which electricity is generated and pulsed into the water. Any fish within the path of the electricfield is temporarily stunned and floats to the surface.5

Health ConsultationMercury Exposure Investigation - Caddo Lake AreaTotal blood mercury (methylmercury and inorganic mercury) levels for the 71 participantsranged from less than ( ) 2 to 15.9 µg/L (micrograms per liter) [Table 2] and followed alognormal distribution with a geometric mean of 2.63 µg/L [Figure 3]. The geometric meanblood mercury levels for males and females were 2.98 µg/L and 2.35 µg/L, respectively.Sixty-eight participants (96 %) indicated they consume fish. Three participants indicated they donot eat fish or have not consumed fish in approximately four years. Participants reported eatingvarious amounts of 11 different types of fish plus frog [Table 3]. Catfish and crappie were themost commonly eaten species [Table 3]. The average mercury content found in catfish andcrappie was 0.219 ppm and 0.263 ppm, respectively [Table 1]. Freshwater drum, which had thehighest average mercury content of 0.913 ppm, was consumed by approximately 13% of theparticipants. Largemouth bass, which had an average mercury level of 0.647 ppm, wasconsumed by approximately 48 % of the participants [Table 3].Participants were asked how often they consumed fish and/or frog. Answers ranged from noconsumption to seven times per week. The majority of participants (29%) indicated theyconsume fish two times a week. Five participants indicated that they consumed fish 7 times aweek. We rank ordered the fish consumption data for all participants (male and femalecombined), males only, and females only and split the data for each group into (low, medium,and high consumption groups). For each tertile we then calculated the average number of fishmeals eaten per week and the average blood mercury concentration. For all participants, theaverage number of fish meals eaten per week for the low, medium, and high consumption tertileswas 0.4, 1.7, and 4.0 meals, respectively [Figure 4]. For males, the average number of fish mealseaten per week for the low, medium, and high consumption tertiles was 0.6, 2.4, and 4.4 meals,respectively [Figure 5]. For females, the average number of fish meals eaten per week for thelow, medium, and high consumption tertiles was 0.4, 1.5, and 3.7 meals, respectively [Figure 6].When fish intake is consistent and prolonged, there is generally a well defined relationshipbetween mercury in the blood and consumption of fish. There was considerable variabilitywithin each of the tertiles likely the result of the uncertainties associated with dietary recall data.Average blood mercury levels did appear to increase with increasing weekly fish consumption[Figures 4, 5, and 6].The laboratory which analyzed the Caddo Lake area samples indicated that the expected range ofblood mercury is 5.0 µg/L. Fourteen participants (10 male and 4 female) had blood mercurylevels greater than ( ) 5.0 µg/L with levels ranging from 5.1 µg/L to 15.9 µg/L. Fishconsumption rates for these participants ranged from once per month to seven times per week.Seven of the participants indicated that they ate largemouth bass and one of the sevenparticipants indicated they also ate freshwater drum [Table 4].6

Health ConsultationMercury Exposure Investigation - Caddo Lake AreaDiscussionPublic Health ImplicationsThe Texas Department of State Health Services periodically makes risk management decisionsregarding the public health implications associated with eating fish and shellfish contaminatedwith methylmercury (MeHg). These decisions can range from the issuance of fish consumptionadvisories to actual prohibitions on the taking of fish. The challenge to health officials is tobalance the known health benefit of consuming more fish in the diet with the known health risksassociated with excess MeHg exposure. Thus, it is important to ensure that risk managementdecisions pertaining to seafood are appropriate and do not do more harm than good. The purposeof this exposure investigation was to evaluate methylmercury exposure in the fish eatingpopulation around Caddo Lake.The ability of fish and seafood to bio-accumulate MeHg is a complex process that involves bothchemical and biological reactions. Small concentrations of inorganic mercury released to theatmosphere, through natural and human mechanisms, will cycle through the environment (air,soil, and water). Under the proper conditions in aquatic systems, inorganic mercury can undergoin-situ bacterial conversion to MeHg, an organic form of mercury. MeHg can move up the foodchain into fish and since they do not readily eliminate MeHg from their bodies, it bioconcentrates in their tissues throughout the course of their lives. Older (longer lived) predatorfish often have the highest concentrations of MeHg in their tissues.Although fish are resistant to the toxic effects of MeHg, people are not. Thus, people who eatfish contaminated with MeHg could be at risk for adverse health effects. Clinical andepidemiological evidence indicates that ingestion of MeHg can result in paresthesias (tinglingfeeling), ataxia (loss of coordination), dysarthria (inability to articulate words), deafness, motorretardation, death, and brain damage in developing fetuses. The developing nervous systemappears to be particularly sensitive to the toxic effects of MeHg and currently is considered themost sensitive endpoint with regard to MeHg toxicity.Consumption of fish is one of the single most significant sources of human exposure to MeHg.Approximately 99 % of the mercury in fish is MeHg. In people, MeHg is easily absorbedthrough the gastrointestinal tract and rapidly enters the blood stream where it is transported toother parts of the body. Ingestion of too much MeHg can result in permanent damage to thebrain and kidneys. In the blood of pregnant women, MeHg can pass into the blood of the fetusand enter the fetal brain. Some MeHg in a nursing mother can be passed to the child through herbreast milk [10]. While the health effects of exposure to MeHg are well documented, there stillis controversy with respect to how much is too much; the most recent “upper safe limit” formercury in human blood is 5.8 µg/L [Table 5]. This is based on the 2001 revision of the USEPA’s reference dose (RfD) for MeHg. EPA’s revised RfD is based on data showing adverseeffects of MeHg exposure on multiple tests of child development. EPA used benchmark dose(BMD) methodology to determine the lower limit on the 5 % response level (BMDL) formultiple tests of neurobehavioral function. With the multiple endpoints they reported BMDLs inthe range of 32 to 79 µg/L in maternal blood for different neuropsychological effects in the7

Health ConsultationMercury Exposure Investigation - Caddo Lake Areaoffspring at 7 years-of-age. EPA used a one compartment model to estimate the daily dosesassociated with these blood levels and used an integrated approach to derive a daily doseequivalent to a maternal blood level of 58 µg/L. At 58 ug/L there is a doubling of the prevalenceof test scores (i.e., from 5 % to 10 %) in the clinically subnormal range. They then applied anuncertainty factor of 10 to account for pharmacokinetic and pharmacodynamic variability anduncertainty to derive the RfD which is equivalent to approximately 5.8 µg/L. Thus, with in uteroexposure, the probability of below normal scores on neurodevelopmental tests increases as bloodlevels increase from 5.8 µg/L to 58 ug/LThe blood mercury levels of the participants in this exposure investigation ( 2.0 - 15.9 µg/L)were comparable to those of the general population ( 5 - 20 µg/L) [10]. However, thegeometric mean blood mercury level for women in this fish eating population (2.35 µg/L) isgreater than the 1.02 µg/L geometric mean reported for women ages 16-49 by the 1999-2000National Health and Nutrition Examination Survey (NHANES) [11, 12] [Table 6]. The bloodmercury levels at the 10th, 25th, 50th, 75th, 90th, and 95th percentiles for women in thisinvestigation also were higher than those reported by NHANES [Table 5]. The five femaleparticipants (14 %) who were of childbearing age (18-44 years) all had blood mercury levelsbelow the 5.8 µg/L level for developmental effects. All participants (male and female) had bloodmercury levels below those normally associated with adverse health effects in adults. Based onthese data we would not expect to see observable adverse effects in this population.Although this is a fish eating population, the observed blood mercury levels are lower than wewould have expected; the variety of fish eaten may be responsible for this observation. Based onthe observed blood mercury levels and the participants self reported frequency of fishconsumption, eating a variety of fish types may be an effective way to manage exposure tomercury.Conclusions1.The geometric mean blood mercury levels measured in this fish eating population washigher than that reported by NHANES for the general population; however, it was lowerthan what we might have expected in people who regularly eat fish taken from a lakewith a known fish mercury problem.2.The five female participants who were of childbearing age all had blood mercury levelsbelow the levels associated with adverse neurodevelopmental effects in children exposedin utero. Additionally, all participants had blood mercury levels below those normallyassociated with adverse health effects in adults.3.Eating a variety of fish, as reported by the participants may be an effective way tomanage exposure to mercury.8

Health ConsultationMercury Exposure Investigation - Caddo Lake AreaPublic Health Action PlanActions Completed1.The DSHS Exposure Assessment and Surveillance Group mailed letters to participantsconcerning their blood mercury test sample results. An explanation of the findings, and ifnecessary, any recommendations to reduce mercury exposure were included in the letter.2.Using information regarding the types of fish consumed and the locations from which thefish were caught, the DSHS Seafood and Aquatic Group, collected and analyzed CaddoLake fish and frog tissue for mercury.Actions Recommended1.Continue to post and maintain advisory signs around Caddo Lake indicating theconsumption of largemouth bass and freshwater drum should be limited due to mercurycontamination. Continue to periodically sample and analyze Caddo Lake fish, especiallylargemouth bass and freshwater drum, for mercury as funds permit.Actions Planned1.Through a Caddo Lake area community meeting, present and explain findings of theinvestigation and summarize results of the blood and fish testing.9

Health ConsultationMercury Exposure Investigation - Caddo Lake AreaAuthors, Technical Advisors, and OrganizationsReport Prepared byNancy IngramCommunity InvolvementDSHS Exposure Investigation and Surveillance GroupTina WalkerHealth EducatorDSHS Exposure Investigation and Surveillance GroupTom EllerbeeEnvironmental SpecialistDSHS Exposure Investigation and Surveillance GroupSusan Prosperie, MS, RSEnvironmental SpecialistDSHS Exposure Investigation and Surveillance GroupRichard Beauchamp, MDToxicologistDSHS Exposure Investigation and Surveillance GroupJohn F. Villanacci, PhD, NREMT-IDirectorDSHS Environmental & Injury Epidemiology and Toxicology BranchJennifer LykeRegional RepresentativeATSDR Region 6George Pettigrew, PESenior Regional RepresentativeATSDR Region 6W. Allen Robison, PhDToxicologistDivision of Health Assessment and ConsultationSuperfund and Program Assessment Branch10

Health ConsultationMercury Exposure Investigation - Caddo Lake AreaReferences1.Texas Parks and Wildlife Department website. Caddo ns. September 2004.2.Texas Parks and Wildlife Department website. History and Nature of Caddo Lake StatePark. html. September 2004.3.Wilson, Jennifer T. U.S. Department of the Interior. U.S. Geological Survey.Occurrence and Trends in Selected Sediment-Associated Contaminants in Caddo Lake,East Texas, 1940-2002. Water-Resources Investigations Report 03-4253. 2003.4.Caddo Lake Institute website. Caddo Lake Institute,Inc. September 2004.5.U.S. Census Bureau website. American Fact Finder Census 2000. September 2004.6.Agency for Toxic Substances and Disease Registry. Public Health Assessment forLonghorn Army Ammunition Plant. Karnack, Harrison County, Texas. CERCLIS No.TX6213820529. U.S. Department of Health and Human Services. July 9, 1999.7.Texas Department of State Health Services. Telephone Communication. Tom Ellerbee,Environmental Health Specialist with Craig Giggleman, U.S. Fish & Wildlife Service.September 29, 2004.8.Texas Department of State Health Services. Seafood Safety Division website. FishAdvisory ADV-12. September 2004.9.Electronic Correspondence. Michael Tennant, Survey Branch Chief, Seafood SafetyDivision, Texas Department of Health to Tom Ellerbee, Environmental Health Specialist,Environmental Toxicology Division, Texas Department of Health. Caddo LakeSampling/Analysis-Questions. August 11, 2004.10.U.S. Department of Health and Human Services. Agency for Toxic Substances andDisease Registry. Toxicological Profile for Mercury. March 1999.11.U.S. Department of Health and Human Services. Centers for Disease Control andPrevention website. National Report on Human Exposure to Environmental Chemicals.January 2003., K.R., Clickner, R.P., and Joseph, C.B. Blood organic mercury and dietarymercury intake: National Health and Nutrition Examination Survey, 1999 and 2000.Environmental Health Perspectives, Online 19 November 2003 at Http://

Health ConsultationMercury Exposure Investigation - Caddo Lake AreaCERTIFICATIONThis Caddo Lake Mercury Exposure Investigation/Health Consultation was prepared by theTexas Department of State Health Services under a cooperative agreement with the Agency forToxic Substances and Disease Registry (ATSDR). It was done in accordance with approvedmethodology and procedures existing at the time the health consultation was initiated. Editorialreview was completed by the Cooperative Agreement partner.Technical Project Officer, CAT, SPAB, DHAC, ATSDRThe Division of Health Assessment and Consultation, ATSDR, has reviewed this public healthconsultation and concurs with its findings.Team Lead CAT, SPAB, DHAC, ATSDR12

Health ConsultationMercury Exposure Investigation - Caddo Lake AreaAppendicesAppendix A: - Acronyms and AbbreviationsAppendix B: - FiguresAppendix C: - Tables13

Health ConsultationMercury

National Wildlife Refuge. The U.S Army retains control of the remainder of the site [7]. On November 2, 1995, due to elevated levels of mercury in fish1, the DSHS issued a consumption advisory for largemouth bass (Micropterus salmoides) and freshwater drum (Aplodinotus grunniens) taken from Caddo Lake. The consumption advisory states that eating